The present disclosure relates to a method and apparatus for regulating a power amplifier for operation in a timeslot data transmission system.
A power amplifier is used particularly in a data transmission system, such as in a mobile radio system. In recent years, a series of standardized transmission systems have been defined for mobile radio systems. In this case, particularly the type of modulation of the information to be transmitted and the type of transmission between a base station and a mobile terminal are defined.
In a transmission system which is used for modulation with a constant amplitude envelope, the output power is jointly determined by the gain of the power amplifier. Modulation with a constant amplitude envelope is used in a transmission system based on the GSM (Global System for Mobile Communication) standard, for example. This has provision for the information which is to be transmitted to be put onto a carrier signal using GMSK—(Gaussian Minimum Shift Keying) Modulation.
In a communication system, it is desirable for bi-directional communication transmission to be possible. By way of example, this is achieved in some communication systems, such as, DECT (Digital Enhanced Cordless Communication), by using Time-Division Duplex (TDD). This involves the transmission being divided into a series of timeslots, with transmission taking place in one direction, for example from a mobile terminal to a base station, during one timeslot. In another timeslot, transmission takes place from the base station to a mobile terminal.
In another form, dividing up the communication into timeslots allows multiple access, so that a plurality of subscribers in the system can communicate with one another or with a jointly used transmission system. Thus, GSM has Time Division Multiple Access (TDMA) defined, in which various mobile terminals in a radio cell communicate with the base station at different times.
On account of the opportunities for time-division duplex and time-division multiple access, these methods are also used in other communication systems, such as wired or optical communication systems.
The technological development of recent decades has made it possible for the manufacturers of mobile terminals to provide ever smaller mobile terminals. Since the size of the terminals is determined by the size of a power reserve, i.e., a battery or a storage battery, among other factors, it is desirable to reduce the power consumption of the mobile terminal. In addition, lower power consumption increases the talking or operating time between charging the power reserve of the mobile terminal. Substantial power consumption in the mobile terminal is caused by the power amplifier, which provides substantial proportions of an output power for the transmission signal. It is therefore desirable to allow the most power-efficient operation of the power amplifier possible.
Secondly, it is necessary for the output power of the power amplifier to be high enough for a base station to receive a signal from the mobile terminal reliably. To this end, the base station frequently prescribes the output power at which the mobile terminal needs to send its signal.
In a mobile terminal, an output signal from the power amplifier is introduced into a radio communication channel by an antenna. The output signal is a radio-frequency signal which is at frequencies between 600 MHz and more than 2.5 GHz. As a result, impedance matching on the antenna plays an important part. If antenna impedance differs from a particular value, portions of the output signal return to the power amplifier via a connection between the power amplifier and the antenna on account of reflections on the antenna. If there is a mismatch in the antenna impedance, a transmission power radiated by the antenna is significantly lower than the output power provided by the power amplifier. This results in low energy efficiency in the power amplifier when there is a mismatch. A mismatch in the antenna impedance can arise randomly when the mobile terminal is being used. By way of example, it is sufficient for a user to touch the antenna.
Without the provision of a safety margin for setting the output power, the mobile terminal cannot behave in accordance with the guidelines of the standard under all conditions which are to be expected. A behavior which does not comply with the standard is undesirable for the network operators and is accordingly avoided by the manufacturers of the mobile terminals. Rather, increased power consumption and hence a shorter operating time for the mobile terminal are accepted.